Solar water heating - Criteria

  
     
 

Application to the home

Solar thermal heating is possible if

  • the roof orientation is south or south west
  • there is little shadow during the day i.e. no tall trees or high buildings to shade the array from direct sunlight for any appreciable part of the day
  • the roof structure is able to carry the extra load of the installation
  • the new system is able to connect to the existing hot water system

Effect of climate

  

The amount of radiation depends upon the position of the sun in the sky as the lower the position the more energy is absorbed by the earth's atmosphere. This gives rise to the observed temperature variations during the day, between summer and winter and between the north and south of any country. The annual mean solar radiation for the UK is shown left.

Whilst on a sunny day, solar radiation can be directly received, on a cloudy day less radiation is received because it is scattered by the water droplets on the clouds. Typical values are shown below.

During summer there is generally sufficient radiation to provide almost all the domestic hot water demand, whilst during the winter the proportion produced by solar radiation is much less. Overall about 50-60% of the annual demand in the UK can be met.

 

Environmental impact

There are no environmental impacts for the solar heating of water and a negligible amount associated with the production of the electricity to pump the water around the collector.

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